sum = 0
up = 2
down = 1

print(f'1 :{up}/{down}')

for i in range(20):
    sum += up / down
    # 下一个数
    temp = up
    up = down + up
    down = temp
    # up = up + down
    # down = up - down
    print(f'{i + 1} :{up}/{down}')

print(f'sum:{sum}')
